This invention relates to phenol/formaldehyde resins and specifically to certain novolac resins useful as binders for glass fiber insulation materials.
In the production of a typical glass fiber insulation material, loose glass fibers usually derived from textile re-work and/or waste, are first garnetted into a loose mat and then mixed with granules of a binder composition with a mean particle size of 10-30 microns, and passed into a mat former in which the binder granules and the glass fibers are intimately mixed and formed into a mat. This mat is then passed into an oven at from 200.degree.-400.degree. C. There the binder is cured and bonds the glass fibers into a coherent mat.
Among the qualities of the binder that are particularly prized by the user are (a) a low level of dustiness so that the work area is not contaminated and resin usage is minimized; (b) good wettability/bonding of the fibers by the resin which in turn contributes to better resin distribution and the lack of undesirable resin stratification; (c) efficiency i.e. acceptable mat properties at lower resin levels, so that no more resin is used than is necessary; (d); good release properties giving an absence of stickiness to metals during forming and curing steps; (e) good electrical conductivity, so as to avoid electrostatic build-up and thereby reduce the need for cleanups and to improve product uniformity; (f) hydrophobicity, (water repellency), so that the cured mat will not be adversely effected (lower "R" value) by absorbed water; (g) long resin shelf life (stability), that is, no resin advancement and less caking tendency during storage; (h) additives with a low level of toxicity and (i) fast curing characteristics so that resin will be completely cured not only in smaller ovens but also at lower temperatures thus generating energy savings.
This last characteristic, fast curing, is important because the lower the oven temperatures, the lower are the emissions. Resin curing characteristics are of great importance in commercial lines because products manufactured from slow curing resins (generally one-stage resins) usually leave the oven while the exothermic curing reaction is still in progress. Due to the excellent insulation properties of the finished product, this accumulated heat can cause fires in warehouses/railroad cars, etc. In fact, it is a common practice in the industry to store the rolls in the production plants for observation before any shipment is done.
The one-stage resins which are the only currently approved resins for this commercial application lack several of the desirable characteristics listed above to some degree and up to now, no known two-stage resin system has become commercial because the performance of such systems is even less satisfactory than that of the one-stage resins.
The present invention describes a two-stage resin binder formulation that is more than usually effective in all the above respects. Moreover the binder formulation of the invention produces cured mats which have displayed good recovery after compression; absence of product degradation, most significantly in terms of loss of thickness upon storage and/or coating operation; water repellency so as to maintain a high "R" value; high quality bottom and top surfaces free from lumpiness and/or fuzziness; and adequate stiffness.